An internal combustion engine-generator system of the type mentioned at the outset generally comprises a plurality of internal combustion engine-generator units, which generate electric power and can be connected to a distribution grid. Additionally, load consumers consuming electric power are connected via the distribution grid, which consume as load the electric power generated by the internal combustion engine-generator units. The above-mentioned internal combustion engine-generator unit comprises an internal combustion engine with variable engine speeds and a generator. Such internal combustion engine-generator systems are used in large vehicles, e.g. land vehicles or watercraft, but also as stationary systems. In general, an internal combustion engine-generator unit has the function of a power generator, which e.g. couples a motor and a generator for driving the generator, perhaps via a transmission, with the generator in turn generating power.
Commonly a diesel engine is operated in a power generator, to the extent possible with constant engine speed. Due to the fact that a diesel engine can also be operated at higher engine speeds than the common 1500 and/or 1800 rpm, and thus can yield more power, it is also common in certain limited operating situations to allow operation with variable engine speeds via power-electric measures. In this case a frequency of the electric power provided by the generator and dependent on the engine speed of the internal combustion engine is first rectified and then inverted into the frequency of the power generator desired for the distribution grid. In particular in such a case, the internal combustion engine, particularly a diesel engine, is operated according to predetermined characteristics, which state the power output allocated to each engine speed. Such characteristics commonly extend at a safe distance from the engine speed or the torque representing the maximum capacity, which can be stated via a so-called DBR and/or MCR-curve of a diesel engine. This way it is ensured that an appropriate power reserve is maintained for the diesel engine, which shall serve to render available sufficient power reserves at the diesel engine for variable loads. However, such an operation of a diesel engine is not optimal with regards to consumption when operated regularly.
For example, from DE 199 37 139 C1 a method is known for controlling an internal combustion engine, which actually shall be operated stationary, in which upon detection of a significant reduction in load at the driven side the start of injection is adjusted to a later point of time. The engine speed limit curve provided here to limit the target injection rate limits the adjustment range in the stationary operating state. From DE 103 02 263 B3 a method is known in which in the stationary operating state the target injection rate is limited via a first engine speed limit curve. Upon detection of a dynamic operating state, a second engine speed limit curve is switched to.
It is ideal to optimally operate an internal combustion engine, particularly a diesel engine, within the scope of an internal combustion engine-generator unit as a part of an internal combustion engine-generator system, for example with relatively good specific fuel consumption and yet still sufficiently strong electric load override.
In an internal combustion engine-generator system with parallel operation of a plurality of internal combustion engine-generator units, also called GENSET, their respective operating points can be generally optimized due to the above-mentioned independence of power output and engine speeds in a diesel engine. In such parallel operation of several power generators for example, the capacity is distributed to the units, e.g. according to the nominal power output of the diesel engines, and load changes are also distributed over the units. In common controls, within the scope of switching on or off, generally the problem of over-oscillation can occur. This can be partially corrected in a so-called “P-level control”, as described for example in DE 10 2004 015 973 B3 of the applicant. Here, higher power output is adjusted by the operator via the increase of the predetermined target engine speed and a higher target injection rate leads to a higher power output of the internal combustion engine. Here, it is also provided that an increase of the predetermined target engine speed causes a shift of the engine speed limit curve to a faster actual engine speed. In one example it is suggested that a governor control curve of the engine speed limit curve can be modified via the “P-level”. Consequently the stationary operating points of the diesel engines of the power generator then show sufficient distance from the limit curve (DBR-curve) so that load increases and load changes can be compensated. The above-mentioned process has been proven for the generally stationary operation and in generally predetermined load changes, which are set for example in standards and regulations.
In general, all of the above-mentioned concepts are suitable only to a limited extent for dynamic, internal combustion engine-generator systems with strong variations in engine speeds, i.e. actually constantly operating for example in transient mode, and the internal combustion engine-generator units networked here.